There is a difference: Demon BoltImpact is the effect that happens when a unit hits an enemy unit with Chain Lightning or something similar. ChimaeraLightningMissile_Fel is like the regular ChimaeraLightningMissile. You insert the model as a projectile for your unit, Chimaera for example, and then you edit Lightning Attack. You change the Art - Lightning Effects to FLBT, then you edit its' missile, which is war3mapImported\ChimaeraLightningMissile_Fel.mdx and then you change Art - Target to use BoltImpact_Fel.mdx
Once I finish the fel lightning package, I'll post it in the model thread, so that everyone can enjoy.